Forbidden Archive

The Forbidden Archive is the Necron reliquary, containing all of the most powerful tools available to the Necron Lord. Due to the difficulty of properly extracting this equipment from the depths of the Necron tombs, only a limited number of artifacts can be exhumed during a single battle.

Tactics

After researching the maximum of 3 upgrades for your Necron Lord, this building becomes useless.
So if you need room for some more Plasma Generators, simply delete the Forbidden Archive.
Or leave it as a decoy and regroup your forces while the enemy attacks this obsolete building. Of course, you could build it near to Obelisks in order to teleport infantry - your opponent will want to attack such an important research building, not knowing that it is already useless.